This invention relates generally to apparatus and methods for injecting sealing balls into a well. The apparatus and method of the present invention use closed loop control to release balls in response to a sensed flow of a fluid which is pumped into a well and which carries the released balls with it.
In the completion of oil and gas wells, it is common practice to conduct a fracturing or other treating procedure. In a typical fracturing procedure, for example, the casing of the well is perforated to admit oil and/or gas into the well and fracturing fluid is then pumped into the well and through these perforations into the formation. Such treatment opens and/or enlarges draining channels in the formation, enhancing the producing ability of the well.
The treating fluid enters those zones of the formation having the highest permeability while the zones of the formation having lower permeabilities, and therefore requiring treatment the most, receive very little or none. It is well known to those skilled in the art to use sealing balls in order to temporarily block off the perforations leading to the higher-permeability zones to divert the treating fluid into the lower-permeability zones. These sealing balls are dispensed into the treating fluid and carried thereby to perforations through which the fluid is passing. The fluid pressure holds the balls in sealing positions thus blocking those perforations and forcing the fluid to other perforations.
Various ball injectors have been disclosed which inject perforation-sealing balls into the well. These units are operated either manually, in which an operator is required to release each ball, or automatically, in which an automatic timer injects a ball at a predetermined rate of time.
One disadvantage of the previous disclosures is that they are open-loop systems which inject balls according to time and not directly according to the amount of treating fluid pumped into the respective well. Thus, the release of a desired number of balls in these open-loop systems depends on there being a constant flow rate, which typically is not the case. That is, when balls are injected at predetermined time intervals, varying fluid flow rates will cause either too many or too few balls to be released relative to the amount of fluid pumped. Releasing too many sealing balls causes perforations to be sealed prematurely before the desired volume of treating fluid can be placed through those perforations. This defeats the purpose of fracturing, that being to enlarge the zones of draining channels. Releasing too few sealing balls presents the same problems which existed before the sealing balls were used, that being the lower-permeability zones receiving insufficient fracturing fluids; this allows more than the desired amount of treating fluid to enter higher flowing perforations. This is wasteful and expensive and can damage the formation.
To overcome the foregoing shortcoming, there is the need for an apparatus and method which can inject balls in relation to the fluid flow amount so that only desired amounts are pumped through perforations before they are blocked off by a desired number of sealing balls.